https://arstechnica.com/gadgets/2020/02/guidemaster-ars-tests-and-picks-the-best-portable-ssds-you-can-buy/

Portable SSDs are a good way to increase the amount of storage you have to preserve digital data and take that data with you wherever you go. These powerful accessories let you pack a huge amount of storage in your daily bag, giving you a place to offload files from your computer or smartphone, a place to access files you only need in certain circumstances, and backup important information on the go.

But the world of portable SSDs is a large one, and deciding on the best device for your needs can be a challenge. It's not just about how small the device is, how durable it is, or how many gigabytes of storage it has—the speed of a portable SSD can heavily influence your satisfaction with it. SSDs in general promise better read and write speeds than HDDs, so you'll see a general increase if you're going from one to the other. However, not all portable SSDs perform the same—even if they advertise similar maximum speeds.